Gemara

(Beraisa - R. Yosi b'Rebbi Yehudah): Beis Hillel are Metamei Dam Neveilah only when there is a Revi'is, since it can congeal to a k'Zayis.

Shabbos 77a (Beraisa - R. Noson): The Shi'ur (to be liable for Hotza'ah) of congealed wine is a k'Zayis.

(Rav Yosef): R. Noson and R. Yosi b'Rebbi Yehudah say the same thing:

Rejection (Abaye): Perhaps R. Noson is Mechayev for a k'Zayis regarding wine, for a Revi'is congeals to a k'Zayis. However, blood is thicker, and even less than a Revi'is is Metamei, for it congeals to a k'Zayis!

Or, perhaps R. Yosi is Metamei a Revi'is of blood because it congeals to a k'Zayis, but wine is thinner, so one is liable for less than a k'Zayis, for it comes from a Revi'is!

Menachos 54b (Beraisa): If one is Torem (designates Terumah or Ma'aser) dates (Stam dates refers to moist dates) on (i.e. to exempt) dried dates, one tithes according to the number (even though dry dates are less than their original volume).

This is like Shmuel, who follows the original volume. It is unlike Rav, who follows the current volume. A tenth of the number is more than a tenth of the volume. One may not give too much Ma'aser!

Question (Beraisa): To be Torem dry dates on dates, one tithes according to the volume.

This is like Rav, who follows the current volume. According to Shmuel, this is too much!

Answer: The Beraisa discusses Terumah Gedolah. In both cases he tithes generously.

Chulin 97b (R. Chanina): When estimating whether there is 60 times as much Heter for Bitul, we include the gravy, the sediment, the solid pieces, and the pot.

Version #1: 'The pot' refers to (the volume of the walls of) the pot itself.

Version #2: 'The pot' refers to the Heter absorbed in the walls of the pot.

Terumos 4:6 (Mishnah): We estimate the basket three times during the year. It is praiseworthy to count, it is praiseworthy to measure, and it is most praiseworthy to weigh.

Rishonim

Perush ha'Mishnayos (Chalah 2:6): The Shi'ur Chalah is about a box 10 (fingers) by 10 by 3.1104 thumbs. If we would measure the weight, it would vary according to the matter measured. The density of w] and barley are not the same. Different kinds of flour have different densities. The Shi'ur of Chalah was not given in weight, rather, in volume. One who gives the Shi'ur in weight errs blatantly, unless he approximates based on a certain species.

Chazon Ish (Mo'ed 39:4): If Chachamim said what is the weight of the Shi'ur of flour or a Revi'is, this is not a Shi'ur Torah. Perush ha'Mishnayos (Chalah 2:6) alludes to this. He permits giving a weight based on wheat flour of a certain city for this year, if it is known to be uniform, to help to clarify the Shi'ur Torah.

Teshuvas ha'Rosh (20:2, cuted in Beis Yosef YD 98 DH Kol she'YEsh): If a k'Zayis of Chelev fell in 29 k'Zeisim of Heter, and a k'Zayis of blood fell in 30 k'Zeisim of Heter, and they mixed with each other, each Isur is Batel, for it cannot give taste to the entire mixture.

Ran (Chulin 34b DH Amar): The Ro'oh said that we consider a Beitzah and a half of gravy like a k'Zayis, for if it would congeal, it would be a k'Zayis. It seems that he learned from Shabbos 77a, which says that a Revi'is of a clear liquid congeals to a k'Zayis. Therefore, if the Isur is congealed, we estimate a Revi'is of gravy like a k'Zayis. Even though Abaye said that perhaps not all liquids are the same, since Rav Yosef was sure, we rely on him, without concern for Abaye's Safek.

Rejection (Ran): The Gemara said that we estimate the gravy. This implies that we estimate it like it is! Chachamim gauged that no Isur gives taste to more than 60 parts, even to gravy! If not, we would need to investigate in every case if the Isur and Heter are thin or thick, and then everything has a different Shi'ur (for how many parts of Heter are required)!

Beis Yosef (YD 98 DH Kasav ha'Ran): Also the Rashba and Ba'al ha'Itur hold like the Ran.

Mordechai (Chulin 7:685, cited in Beis Yosef YD 98 DH u'Mah she'Chasav Lefichach): Avi ha'Ezri says that to estimate if we have 60 times as much Heter, we take a (big) Kli full of water, fill the forbidden Kli with that water, and put it in the big Kli. The water that spills out is the amount (volume - PF) of the walls of the forbidden Kli. Afterwards we measure the water used to be Mevatel it, to see if it is 60 times as much.

Rashi (108b DH Chetzi): To measure a k'Zayis of wine or milk or any liquid, we bring a cup full of liquid, and put an olive in it. The liquid that flows out is a k'Zayis. This is from the a Tosefta in Nazir (Nazir 4:1).

Divrei Chamudos (Chulin 7:113):). The Tosefta is difficult for the Rosh (it seems that the text should say 'the Ro'oh' - PF). The Ran says that we estimate based on water, like Rashi says, or together with estimation, like Perush ha'Mishnayos says.

Poskim

Pri Chodosh 99:4(6): I saw some weigh to determine whether there is 60 times as much Heter as Isur. They err. Sometimes this is too lenient or too stringent. We measure only based on volume. Rashi and Tosfos (Sukah 6a DH Gefen) say so; this is based on a Tosefta in Nazir. If a k'Zayis of milk fell in a pot with much gravy and a little meat, the gravy is less dense than the milk. It is possible that there is 60 times as much volume of Heter as Isur, but not even 50 times as much weight. If we weigh, we will be stringent, but really it is permitted. The Torah is concerned for the money of Yisrael! If the pot has many bones and little gravy, one might permit what is forbidden, for the bones are heavier (denser) than milk, and 40 k'Zeisim of bones might weigh 60 times as much as a k'Zayis of milk. Rather, one must estimate the volume. One who wants to weigh must do so according to the density of the Isur and Heter. One may not rely totally on the weight. The Ro'oh counts a Beitzah and a half of gravy like a k'Zayis, but the Rashba and Ran disagree. Also Ba'al ha'Itur says that a k'Zayis of gravy suffices to be Mevatel a k'Zayis of meat. (I.e. it counts like a k'Zayis towards the calculation of 60 k'Zeisim for Bitul - PF.) People conduct like this.

Yad Avraham: Minchas Yakov (85:58) says that we do not estimate 60 through weight, since not everything has the same density, so one who weighs, errs.

Sha'ar Efrayim (51): A case occurred in which Reuven bought 15 Akams (a unit of weight) of meat in a Nochri meat market, and added another quarter Akam to make the scale tip. After salting, they realized that the extra quarter Akam was Tereifah. It is evident that the Kosher meat is not 60 times the volume of the Tereifah. If we would measure based on weight, there is 60 times for Bitul. Some Gedolei ha'Dor say that the weight is primary. Some forbid, because we see that there are not 60 times as much (volume) for Bitul.

Sha'ar Efrayim: Seemingly, Terumos 4:6 proves that we rely on weight. It connotes that weighing is best whether this adds or subtracts, i.e. he initially measured the produce and separated Ma'aser, and now weighs and finds that the Ma'aser is less than a 10th. He adds to the Ma'aser so it will be a 10th. We are not concerned for giving too much Ma'aser. If he did not complete the Shi'ur, his produce is still Tevel. Likewise, if he weighs and finds that the Ma'aser is more than a 10th, he removes some so it will be a 10th, and we permit his Tevel. We are not concerned for giving too much Ma'aser. If he did not complete the Shi'ur, his produce is still Tevel. If so, we should say similarly regarding the meat. One could explain that the Mishnah refers to a case just like the meat, i.e. one bought a weight of Peros, separated Ma'aser based on the weight, and later found that the volume of the Ma'aser is more or less than a 10th of the volume of the Peros. The Mishnah teaches that weighing is best (so we rely on it). The Mishnah does not connote that he weighed first, but in any case the law is true. Do not say that the Mishnah means that weighing is best only to add (separate more) Ma'aser. If so, you must also say that measuring is better than counting only to add, but not to deduct. Menachos 54 teaches unlike this! Actually, Menachos 54 proves that measuring is better in order to add, but not to deduct. Since it is a 10th regarding measure, we are not concerned if it is more than a 10th of the number. Likewise, weighing is better only to add. Also regarding meat, we do not follow the weight if there is not 60 times based on estimation and volume. Even regarding Min b'Mino, measuring is better than weighing, for perhaps some are denser than others, like the Rambam says. All the more so one may not rely on weight for Min b'Eino Mino!

Sha'ar Efrayim (DH v'Ra'ayah): The Tur (YD 98) says that if a pot had 59 k'Zeisim of Heter, and one k'Zayis of Chelev and one k'Zayis of blood fell in, they join with the Heter to be Mevatel each other. Surely, a k'Zayis of Chelev does not weigh the same as a k'Zayis of blood. Even so, either helps to be Mevatel the other (even the one that weighs more). This shows that we totally ignore the weight. The source for this law is invalid. The Tur learned from Teshuvas ha'Rosh. The Beis Yosef says that the Rosh learned from Rav Papa (Zevachim 78a), who holds that Isurim are Mevatel each other. The Rambam rules like R. Elazar (79a), who disagrees! It is difficult to say that the Rosh and Tur rules like Rav Papa. The Kesef Mishneh brought from the Yerushalmi that R. Yochanan holds like Rav Papa, so the Halachah follows him! Also, the Rosh, Tur or one of the Poskim should have said that the Rambam disagrees! Rather, the Rosh learned from Orlah and Kil'ayim, which are Mevatel each other. In conclusion, we follow the volume, and not the weight.

Avodas ha'Gershoni (30): One could say that perhaps we follow the volume only regarding a Kli, for then we cannot follow the weight, since the walls of the Kli do not forbid. Only the Isur absorbed inside forbids (and the absorbed Isur depends only on volume)! This would explain why Avi ha'Ezri and the Roke'ach taught this regarding Kelim! However, perhaps they taught about Kelim because this is a bigger Chidush. Regarding Isur itself, it is clear how we measure. However, there is a clear proof from the Ran that it depends on volume. Also in Chulin, one opinion says that to estimate whether there are 60 parts of Heter for Bitul, we include the pot, i.e. the pot itself. This cannot mean its weight, for if so, if equal amounts of Isur fell into pots of the same size but made of different metals, sometimes one is forbidden and the other is permitted. This is absurd. The pot has no taste, so surely its weight is irrelevant!

Pischei Teshuvah (98:2): Sha'ar Efrayim, Avodas ha'Gershoni and the Rashbatz' son all say that we follow the volume. Chinuch Beis Yehudah says that if the Isur and Heter have the same density, i.e. they are the same Min, we may measure both or weigh both. If one of them has a hollow, and we would need to compress it, then weighing is better, lest he not compress it properly. Regarding two Minim, even if there is a hollow, one must (compress it and) measure. Beis Efrayim (YD 36) says that if a congealed k'Zayis fell into a cooked food, e.g. lard into milk or butter into mat, even though it immediately melts when it falls in and becomes a Revi'is, it suffices to have 60 k'Zeisim of Heter to be Mevatel it, even though the Isur inflated. If it melted before it fell in, perhaps mid'Rabanan we require 60 Reviyos, for a Revi'is of Isur was recognized by itself.

Pischei Teshuvah (2, citing the Rambam (Pe'er ha'Dor 65)): We may tell an Am ha'Aretz that Isur is Batel in 60 parts of Heter. Mid'Oraisa, Isur is Batel in a majority. It is a decree mid'Rabanan to require 60, so we need not decree further lest the Am ha'Aretz be more lenient.

Pischei Teshuvah: The Shach (2) explains that the Rambam holds that Ta'am k'Ikar (if an Isur can be tasted in a mixture, the mixture is forbidden) is not mid'Oraisa. If so, since we hold that Ta'am k'Ikar is mid'Oraisa, it should be forbidden to tell an Am ha'Aretz that Isur is Batel in 60! This requires investigation, for we never heard anyone say so.